A comedy classic film, The Seven Year Itch (1955) starring Marilyn Monroe, Tom Ewell, and directed by Billy Wilder, satirised the tendency of men to "stray" from their wives after seven years of marriage.

Is there really a seven year itch? According to research, it is more likely the four year itch. Dr Helen Fisher, an anthropologist at the Centre for Human Evolutionary Studies in the Department of Anthropology at Rutgers University, studied 62 groups of people from different cultures throughout the world.

She found that, overall, divorce rates peak after about four years, not seven. As for the inevitability of the seven year itch occurring in relationships? This is unclear. In the film, the psychiatrist says to Tom Ewell: "Sir, when you itch, the tendency is to scratch."

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to s.juan@edfac.usyd.edu.au